1. Field of the Invention
The present invention relates to a thermosensitive recording material employing color formation by the chemical reaction between an electron donor compound and electron acceptor compound and more particularly to an improved thermosensitive recording material having excellent matching property on a thermal head.
2. Discussion of the Background
There are conventionally proposed various materials which utilize the coloring reaction between a colorless or light-colored leuco dye and a color developer capable of inducing color formation in the leuco dye upon application of heat or pressure thereto when brought into contact with the leuco dye.
A thermosensitive recording material of this type is useable as a recording material for a computer, facsimile apparatus, ticket vending apparatus, label printer, and recorder because it has the advantages that complicated processes such as development and image fixing are not required, recording can be performed, using a relatively simple apparatus, no noise is generated during the development, and the manufacturing cost is low.
In such a thermosensitive recording material, colorless or light-colored leuco dyes having a lactone, lactam, or spiropyran ring are used as coloring dyes, and organic acids or phenolic materials are conventionally employed as color developers. The thermosensitive recording material using the above-mentioned leuco dye and color developer is widely used because the produced images have a high density and the whiteness of the background is high.
These thermosensitive recording materials are generally manufactured by coating the coloring dyes and the coloring developers on a base, such as plain paper.
In recent years, in response to an increasing demand for producing high quality images, in many cases, the surface smoothness of the color developing layer is increased by the provision of an undercoat layer under the color developing layer.
Furthermore, in accordance with the diversification of the application of the thermosensitive recording material, a plastic film having high surface smoothness is used instead of plain paper as a base sheet.
Especially at the case of OHP, for purpose of producing the thermosensitive recording material having a transparent property, and a high quality image, a base sheet such as plastic film having a high surface smoothness is used, and an equally smooth coating layer is formed on the base sheet. But, a structure of the thermosensitive recording materials is not substantially different from those used with plain paper as a base sheet.
These thermosensitive recording materials can be brought into contact with the thermal head so closely that the thermosensitive recording materials exhibit excellent uniformity in coloring.
However, excellent contact between the thermosensitive recording material and the thermal head causes a sticking problem.
In order to prevent such sticking problem and also to improve head matching property, materials such as inorganic pigments are added to the thermosensitive recording materials.
However, such materials added to the recording material cause defacement of the thermal head.
The plastic film employed as the base sheet is highly electrostatically charged so that dust or less are caught on the surface of the thermosensitive recording material. Such dust, or less, is released from the molten coated layer of the recording material at printing.
The dust, or lees, is caught between the thermosensitive recording material and thermal head. This causes a problem in which a part of the developed image is developed with stripes. The stripe is called a white strip at this portion.
In conventional technology, a proposal has been made that an irregular shape filler is employed in a protective layer of the thermosensitive recording material in order to improve the sticking phenomenon, as disclosed in Japanese Laid-Open Patent Application 61-225096. Moreover, a thermosensitive recording material which has a protective layer employing a spherical filler is proposed. However, effect of preventing the white stripes is not completely successful because the surface of the protective layer cannot be enough roughed only by the spherical filler.
On the other hand, using only an irregular shaped filler, the problem of thermal head defacement cannot be solved.
In other words, as long as one of the spherical filler or the irregular filler is used, the problem of thermal head defacement and the white stripe and sicking problem cannot be solved at the same time.